ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Hurricane Norma Discussion Number 5 NWS National Hurricane Center Miami FL EP172023 300 PM MDT Wed Oct 18 2023 Norma continues to rapidly intensify this afternoon. Intense inner-core convection has resulted in a ring of very cold cloud tops surrounding the center of the cyclone, and a ragged eye has emerged in recent visible images of Norma. The latest subjective Dvorak classifications from TAFB and SAB were T4.5/77 kt and T4.0/65 kt, respectively, and the UW-CIMSS objective ADT and AiDT estimates are around 70 kt. The initial intensity is raised to 70 kt based on a blend of these data, which makes Norma a hurricane. Norma has rapidly strengthened by 30 kt during the past 24 h. The warm waters, weak to moderate vertical shear, and moist and unstable environment around Norma appear favorable for more steady to rapid strengthening through early Thursday. The NHC forecast closely follows the regional hurricane models in the near term and shows Norma becoming a major hurricane on Thursday. Thereafter, an increase in southwesterly shear should begin to disrupt the vertical structure of Norma and cause some weakening on Friday and through the weekend. The NHC forecast lies on the higher end of the guidance, closest to HCCA, during the latter part of the period. Recent microwave and scatterometer fixes indicate that Norma is moving northward (350/7 kt). A northward to north-northwestward motion is expected for the next couple of days or so while the storm moves around a weak ridge to its east. The track models are in good agreement on this part of the forecast, and the updated NHC track forecast is faster than the previous one through 72 h, following the latest HCCA aid. There remains a significant spread in the track guidance at days 3-5. The GFS and regional hurricane models (HAFS, HWRF, HMON) show a northward motion near the southern tip of Baja this weekend, followed by a northeastward motion toward the coast of western Mexico. Other global models (ECMWF, UKMET, Canadian) show a shallower Norma stalling or meandering to the southwest of Baja. The vertical depth and structure of Norma will likely play a major role in its long-term track, and there is above average uncertainty in this part of the track forecast. For now, the NHC forecast remains closer to the stronger GFS-based guidance, although not as fast as the deterministic GFS solution. Given the uncertainty described above, it is difficult to pinpoint the extent or magnitude of potential impacts to portions of Baja California or western Mexico over the weekend. Interests in these areas should closely monitor the latest forecast updates, as more significant track or intensity adjustments could be required in future advisories. Key Messages: 1. Norma is forecast to continue rapidly strengthening through Thursday while it passes well offshore of southwestern Mexico. 2. There remains greater than normal uncertainty in the track and intensity forecasts for Norma later this week and this weekend while it approaches the Baja California peninsula and western Mexico. Regardless, there is an increasing threat of wind and rainfall impacts to southern portions of Baja California Sur by Saturday, and watches could be required there tonight or on Thursday. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 15.6N 108.0W 70 KT 80 MPH 12H 19/0600Z 16.6N 108.1W 85 KT 100 MPH 24H 19/1800Z 17.7N 108.3W 100 KT 115 MPH 36H 20/0600Z 18.7N 108.7W 95 KT 110 MPH 48H 20/1800Z 19.6N 109.1W 85 KT 100 MPH 60H 21/0600Z 20.8N 109.7W 75 KT 85 MPH 72H 21/1800Z 22.1N 110.0W 70 KT 80 MPH 96H 22/1800Z 22.7N 109.9W 65 KT 75 MPH 120H 23/1800Z 24.0N 109.0W 50 KT 60 MPH $$ Forecaster Reinhart NNNN